During start-up or shut-down operation, a certain localized volume of the individual wheel experiences higher or colder temperature than the bulk of the wheel. This induces high temperature gradient resulting in high localized thermal stress along with wheel dishing, which are detriment to not only low cycle fatigue and damage tolerance capability of the wheel but also transient wheel to wheel behavior. In order to reduce temperature gradient, the unit rotor wheels require a secondary flow system to cool/heat the bulk of the wheel during transient operation.
In a gas turbine, the unit rotor during its full range of operation experiences temperatures higher than the material capability. As such, the rotor components are subject to low cycle fatigue, embrittlement and creep issues, which are detrimental to the performance of the system. The unit rotor wheels require a thermal management system to cool/heat the wheels during full range of operation.
In gas turbine engines it is typical to bleed air from the compressor(s) and to supply the bleed air to the turbine(s) of the gas turbine engine in order to carry out sealing and thermal management of the turbine(s). The bleed air must be supplied to the turbine(s) from the compressor(s) with minimum pressure loss so that it has sufficient pressure to provide cooling air and give sealing at the turbine(s).
In one bleed arrangement the bleed air is bled from the compressor(s) generally in a radially inward direction and is then supplied in a downstream direction through the center of the engine, for example through drive shafts or other suitable means, to the turbine(s). The bleed air is passed generally radially through a vortex reducer in order to ensure that there is a minimum pressure loss in the bleed air. The axial flow compressor comprises a rotor having a plurality of stages of circumferentially spaced radially outwardly extending rotor blades and a casing surrounding and spaced from the rotor and rotor blades. The rotor comprises at least two axially adjacent rotor discs defining a chamber therebetween and an air bleed integral with the rotor arranged to bleed a portion of air from the compressor and supply it radially inwardly to the chamber. The two axially adjacent rotor discs have opposed radially extending surfaces, at least one of the opposed radially extending surfaces is contoured to direct the bleed air radially inwardly to prevent the formation of a free vortex within the chamber and thereby reduce pressure losses in the bleed air flowing through the chamber.
The contouring of at least one of the radially extending surfaces may comprise a plurality of circumferentially spaced radially extending vanes. The vanes extend axially from at least one of the opposed radially extending surfaces by a substantially small proportion of the axial distance between the opposed radially extending surfaces of the adjacent rotor discs.